Flame retardant polymeric compositions

ABSTRACT

The present invention relates to improved polymeric compositions based on ethylene-vinyl ester and ethylene-alkyl acrylate copolymers which can be crosslinked to provide insulation coatings for wire and cable products. The copolymer compositions contain a hydrated inorganic filler, an alkoxysilane, an antioxidant and a polymeric processing additive. Organic peroxides are preferably employed to facilitate crosslinking. An improved method for providing the improved compositions and electrical conductors coated with the crosslinkable polymeric compositions are also provided by the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 07/921,617now U.S. Pat. No. 5,225,469, filed Aug. 3, 1992, which is a continuationof application Ser. No. 07/562,762, filed Aug. 3, 1990, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to polymeric compositions which are readilycrosslinkable to produce heat resistant and flame resistant productsuseful in the production of coated wire and cable products as well asfilm sheet and molded products. More particularly, the invention relatesto crosslinkable ethylene-vinyl ester and ethylene-alkyl acrylatecopolymers which during processing, i.e., in the uncrosslinked state,exhibit improved scorch resistance and improved processability and,after crosslinking, exhibit improved resistance to degradation by heataging.

2. Description of the Prior Art

One of the most important uses of fire resistant polymer compositions isfor wire and cable insulation. In electrical environments bothinsulating and fire resistant properties are considered to be necessary.For flame resistance, extrudable compositions available to the wire andcable art were at one time required to contain halogenated polymers,such as chlorinated polyethylene, polyvinyl chloride, chlorinatedpolybutadiene, chlorinated paraffin, etc., together with antimonytrioxide. It was necessary that both components be present in sizablequantities. Alternatively, a coating of chlorosulfonated polyethylenepaint was applied to a nonflame retardant insulating compound whichrequired an additional manufacturing operation.

In certain applications a problem existed in that electrical failuresoccurred due to migration of the organic insulating component used. Theproblem was solved through the addition of hydrated alumina tocompositions whose organic binder consisted of butyl rubber, epoxyresins or polyester resins. Such compositions are disclosed in Kessel etal U.S. Pat. Nos. 2,997,526, 2,997,527, and 2,997,528. Thesecompositions, however, failed to possess an acceptable balance ofprocessability and extrudability characteristics, physical andelectrical properties, heat resistance and flame resistance.Furthermore, these compositions exhibited unacceptable tensile strength,elongation and percent elongation after aging.

Fire retarding polymeric compositions exhibiting improved moisture andheat resistance comprised of a crosslinkable polymer, such asethylene-vinyl acetate copolymer, one or more silanes and one or morehydrated inorganic fillers have found wide acceptance in the wire andcable industry. Such compositions are disclosed in U.S. Pat. Nos.3,832,326 and 3,922,442 to North et al and U.S. Pat. Nos. 4,349,605 and4,381,362 to Biggs et al. Besides the crosslinkable polymer, silane andhydrated filler, additives such as pigments, stabilizers, lubricants,and antioxidants are typically incorporated. These formulatedcompositions exhibit a unique balance of processability, improvedphysical and electrical properties together with a high degree of flameand fire retardance. Moreover, these highly desirable results areachieved (a) without the use of halogenated polymers, such as polyvinylchloride and chlorosulfonated polyethylene, thereby eliminatingpotential for generating dangerous hydrogen chloride fumes; (b) withoutthe use of carbon black thereby making it possible to formulate coloredinsulations; (c) without the application of any flame retardant coatingsthereby eliminating the need for an additional step in manufacturingoperations after the insulating compound is extruded onto the conductor;and (d) without the use of antimony trioxide thereby eliminating theneed to use a substantial quantity of an expensive compoundingingredient.

The compositions of North et al and Biggs et al find particular use aswhite and colored insulation compositions which can be extruded overmetal, e.g., copper or aluminum, conductors to provide a single layerinsulating and jacketing composition which meets the automotive primarySAE J1128 standards and UL 125° C. appliance wire SIS standards. Theseinsulating compositions are particular useful for the insulation ofswitchboard wire, appliance wire and automotive wire where a uniquecombination of superior electrical properties combined with resistanceto the degradative effects of heat and flame are essential and where lowsmoke density and non-corrosive fumes are desirable.

Antioxidants disclosed to be useful for the North et al and Biggs et alcompositions include polymerized 1,2-dihydro-2,2,4-trimethyl quinoline,distearyl-3,3'-thiodiproponate (DSTDP), and combinations of DSTDP withhindered phenols, such astetrakis(methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)) methane.Lubricants which are disclosed include fatty acid soaps, such as calciumstearate and aluminum stearate, silicone oils, long chain aliphaticamides, natural and synthetic waxes and low molecular weightpolyethylenes. A combination of lauric acid and ethylene-bis-stearamideis disclosed to be an especially useful lubricant.

Low molecular weight products which are mixtures of light-coloredaliphatic resins having molecular weights below 2000 are used asprocessing modifiers for plastic compounds. Literature for theseprocessing agents indicates that they possess a natural tackiness atprocessing temperatures which facilitates uniform blending of highlyfilled polymer compositions. It is recognized within the industry thatif compounding ingredients are not uniformly dispersed, physicalproperties of the resulting compositions are adversely affected. Theseprocessing agents are further indicated to provide some viscosityreduction during processing to improve flow characteristics and aresuggested for use with TPO compounds, flame retardant formulations andfilled polymeric systems. There is no suggestion, however, that thealiphatic resin processing agents can be utilized in crosslinkableethylene-vinyl ester copolymer compositions of the type disclosed byNorth et al and Biggs et al containing a silane and hydrated inorganicfiller or that significant advantages in the crosslinked product willresult therefrom.

It is an object of this invention to provide improved crosslinkableflame retardant polymeric compositions based on ethylene-vinyl estercopolymers and ethylene-alkyl acrylate copolymers which exhibit superiorprocessing characteristics and have significantly improved resistance toscorch.

It is a further object to provide crosslinked compositions which exhibitimproved resistance to oxidative degradation.

SUMMARY OF THE INVENTION

In accordance with the present invention these and other objectives arerealized by the use of a polymeric processing agent, by itself or incombination with other known processing additives. The utilization ofthe polymeric processing agent substantially extends scorch time duringprocessing of the compositions without adversely affecting the cure rateand the physical properties of the crosslinked product. Scorch retarderstypically have a detrimental effect on the cure rate, degree of cure,cured physical properties or a combination of these parameters.Additionally, the resulting crosslinked compositions unexpectedlyexhibit significantly improved resistance to degradation by heat aging.

The crosslinkable polymeric compositions of the present invention arecomprised of (1) a polymer selected from the group consisting ofcopolymers of ethylene and vinyl esters of C₂₋₆ aliphatic carboxylicacids, copolymers of ethylene and C₁₋₆ alkyl acrylates, copolymers ofethylene and C₁₋₆ alkyl methacrylates, or mixtures thereof; (2) 80 to400 phr hydrated inorganic filler; (3) 0.5 to 5 phr of an alkoxysilane;(4) 0.5 to 8 phr antioxidant; and (5) 0.25 to 8 phr of a low molecularweight polymeric processing additive. Optionally, from 0.25 to 5 phr ofa second processing additive selected from the group consisting of afatty acid, a calcium soap of a fatty acid, an aluminum soap of fattyacid, a fatty acid amide, a mixture of fatty acids and fatty acidamides, a natural or synthetic wax or a low molecular weightpolyethylene will also be present. In a particularly useful embodimentof the invention the formulation will also contain from 1 to 8 phr of achemical crosslinking agent, preferably an organic peroxide. The lowmolecular weight polymeric processing additive preferably is a mixtureof a hydrocarbon resin derived from cracked petroleum distillates and anethylene-vinyl ester copolymer resin.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to improved polymeric compositionscomprising copolymers of ethylene and a vinyl ester of an aliphaticcarboxylic acid, an alkyl acrylate or an alkyl methacrylate, a silane,and a hydrated inorganic filler. In addition to the foregoing, thecompositions also contain an antioxidant or combination of antioxidantsand a low molecular weight polymeric processing additive. Optionally,other processing agents, such as a fatty acid and/or fatty acidderivative, and crosslinking agents, such as organic peroxides, can alsobe present in the formulation. By the use of the polymeric processingagents, it is possible to significantly increase the scorch resistanceof the uncured composition during processing and, after crosslinking, toobtain products which exhibit a marked increase in heat stability. Thecompositions of this invention are crosslinkable and find particularutility as wire and cable insulation.

The terms "crosslink" and "cure" and their derivative forms are employedsynonymously herein and are ascribed their normal art recognizedmeaning, i.e., they denote the formation of primary valence bondsbetween polymer molecules. Scorching is used in the conventional senseto denote premature crosslinking of the compositions during processing.

Controlled crosslinking can be accomplished using any of the knownprocedures such as chemical means including peroxide crosslinking orsilane crosslinking; by radiation using cobalt-60, accelerators, β-rays,γ-rays, electrons, X-rays, etc.; or thermally. The basic procedures forcrosslinking polymers are well known to the art. All parts andpercentages referred to in the specification and claims which follow areon a weight basis unless otherwise indicated.

THE ETHYLENE COPOLYMER

The polymeric component of the present compositions is a copolymer ofethylene and a comonomer which may be a vinyl ester or an alkylacrylate, the latter being used in the generic sense to encompass estersof both acrylic and methacrylic acid. The vinyl ester may be a vinylester of a C₂ -C₆ aliphatic carboxylic acid, such as vinyl acetate,vinyl propionate, vinyl butyrate, vinyl pentanoate or vinyl hexanoate.The acrylates may be any of the C₁ -C₆ alkyl esters of acrylic ormethacrylic acid including, for example, methyl, ethyl, propyl, butyl,pentyl or hexyl acrylate or methacrylate.

A preferred copolymer comprising the polymeric component of thisinvention is an ethylene-vinyl acetate copolymer (EVA) containing about9% to about 45% and, more preferably, 9% to about 30%, vinyl acetate,with the balance being ethylene. Terpolymers of ethylene, vinyl acetateand other known olefinic monomers polymerizable therewith can also beemployed. Generally, if a third monomer is present it will notconstitute more than about 15% of the polymer composition.

Another preferred copolymer is derived from the copolymerization ofethylene and butyl acrylate. Useful ethylene-butyl acrylate copolymers(EBA) will contain about 10% to about 45% and, more preferably, 20% to40% butyl acrylate--the balance being ethylene. n-Butyl acrylate is apreferred comonomer.

Blends of EVA and EBA can also be advantageously utilized. The EVA willgenerally constitute the major component of the blend but this is notnecessary. The EVA will most typically constitute greater than 75% ofthe blend.

It is also possible to include minor proportions of other crosslinkablepolymers or copolymers in the composition of this invention; however,ethylene copolymers as described above should comprise at least 50% ofthe total polymers present. Representative of such minor polymericcomponents which can be used in such embodiments include polyethylene,polypropylene, ethylene-propylene copolymers and terpolymers, and thelike. Low density polyethylene and linear low density polyethylenehaving melt indexes from 0.5 to 5 provide particularly desirable blendswhen present in amounts of 30% or less, based on the total polymer.

The ethylene copolymers and blends thereof will typically have meltindexes from 0.1 to 7 g/10 min. The EVA copolymers will usually have amelt index from about 0.5 to 5 whereas the melt index of EBA copolymersgenerally ranges from 0.1 to 3.

THE HYDRATED INORGANIC FILLER

To obtain the superior balance of properties necessary for wire andcable applications, it is necessary that a hydrated inorganic filler beused in formulating the polymeric compositions. The fillers used in thepresent invention are hydrated inorganic fillers, e.g., hydratedaluminum oxides (Al₂ O₃.H₂ O or Al(OH)₃), hydrated magnesia, hydratedcalcium silicate, hydrated magnesium carbonates, or the like. Of thesecompounds, hydrated alumina is most advantageously employed. The waterof hydration present in the inorganic filler must be capable of beingreleased during the application of heat sufficient to cause combustionor ignition of the ethylene copolymers. While minor amounts of othertypes of fillers may be tolerated, large amounts of such filler cannotbe utilized.

Since the water of hydration chemically bound to the inorganic filler isreleased endothermically, the hydrated inorganic filler imparts flameretardance. In fact, they increase flame retardance to a far greaterdegree than other fillers previously used by the art to impart flameretardance to insulation, e.g., carbon black, clays, titanium dioxide,etc. What is even more surprising is that flame retardance is combinedwith excellent electrical insulation properties at the high fillerloadings used. The filler size should be in accordance with those sizesused by the prior art.

THE SILANE COMPONENT

One or more alkoxy silanes comprise the second component of the improvedcompositions of the present invention. Any alkoxy silane can be usedwhich does not adversely affect the desired balance of properties andwhich facilitates binding the polymer and inorganic filler with theproviso that the silane can not be combustible or degrade during polymerprocessing or interfere with polymer crosslinking.

Alkoxysilanes used in forming the insulating compositions include loweralkyl-, alkenyl-, alkynyl-, and aryl-alkoxysilanes containing from 1 to3 alkoxy substituents having from 1 to 6 and, more preferably, 1 to 3carbon atoms. Alkoxysilanes having 2 or 3 C₁₋₃ alkoxy substituents, e.g.methoxy, ethoxy, propoxy or combinations thereof, are particularlyadvantageous. Illustrative silanes include methyltriethoxysilane,methyltris(2-methoxyethoxy)silane, dimethyldiethoxysilane,ethyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane,phenyltris(2-methoxyethoxy)silane, vinyltrimethoxysilane andvinyltriethoxysilane, and gammamethacryloxypropyltrimethoxysilane.

It is preferred to use vinyl alkoxysilanes for best results. Of thevinyl alkoxysilanes, gammamethacryloxypropyltrimethoxysilane of theformula ##STR1## vinyltris(2-methoxyethoxy)silane of the formula

    H.sub.2 C═CHSi(OCH.sub.2 CH.sub.2 OCH.sub.3).sub.3 ;

vinyltrimethoxysilane of the formula

    H.sub.2 C═CHSi(OCH.sub.3).sub.3 ; and

vinyltriethoxysilane of the formula

    H.sub.2 C═CHSi(OCH.sub.2 CH.sub.3).sub.3

are especially useful. Vinyltrimethoxysilane is particularlyadvantageous for use in the improved compositions of the invention.

THE ANTIOXIDANT

Conventional antioxidants, such as those known to this art, can beutilized for this purpose. For example, polymerized1,2-dihydro-2,2,4-trimethyl quinoline and tris(3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate can be employed. Various thio compounds andhindered phenols, such as those disclosed in U.S. Pat. No. 4,381,362also provide effective stabilization. Combinations of these latterantioxidants have been demonstrated to be particularly effective andmake it possible for the resulting compositions to pass the CanadianStandards Association (CSA) varnish test. Combinations ofdistearyl-3,3'-thiodipropionate (DSTDP) andtetrakis(methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)) methane aremost notable in this regard. The CSA test is described in detail in theabove-noted reference.

In addition to the foregoing, various other thio compounds, such asdilauryl-3,3'-thiodipropionate, dimyristylthiodipropionate,ditridecylthiodipropionate, bis alkyl sulfides, and hindered phenols,such as 2,6-di-t-butyl-p-cresol, octadecyl3,5-di-t-butyl-4-hydroxyhydrocinnamate, 2,2'-methylenebis(6-t-butyl-4-methylphenol), 4,4'-butylidene bis(6-t-butyl-3-methylphenol), 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, and 2,2'-methylene bis(4-methyl-6-t-butylphenol) can be used.

Also, other antioxidants and stabilizers known to the art for thestabilization of polyolefin resins can be utilized. These can beemployed alone or together with the above noted antioxidants orantioxidant systems. Such stabilizers include ultraviolet lightstabilizers of the hindered amine, benzophenone or nickel type.Antioxidants and stabilizers utilized should not have a detrimentaleffect on polymer crosslinking.

In a particularly useful embodiment of this invention, a bis alkylsulfide is employed in combination with tetrakis (methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)) methane. By using wire andcable formulations containing this combination of antioxidants,particularly when employed at a ratio from 1.5:1 to 3:1(sulfide:phenol), it is possible to significantly reduce and in somecases completely eliminate undesirable discoloration of the conductor.The use of certain widely used thio antioxidants, such as DSTDP, ininsulation formulations, produces undesirable discoloration of thesurface of the copper conductor under certain processing conditions. Thepresence of even slight discoloration or tarnish on the surface of thecopper wire can interfere with the ability to produce sound connectionsby soldering. A fresh clean wire surface after stripping is particularlydesirable in automated soldering operations.

Useful bis alkyl sulfides are commercially available. One such productis commercially available under the designation ANOXSYN™442.

THE PROCESSING ADDITIVES

The use of additives to facilitate processing of filled polymercompositions, in general, and, more specifically, the crosslinkableflame retardant polymeric compositions of the type encompassed by theinvention is well known. Even though the role which various processadditives play is not clearly understood and subject to considerablespeculation and discussion, i.e. whether they are internal or externallubricants, whether they coat or bind the filler, etc., they arenevertheless considered to be essential for efficient mixing of thecompounding ingredients and to achieve uniform, trouble-free extrusionof the formulated composition onto the wire and cable.

One or more processing aids, i.e., lubricants, is required in theformulation of the crosslinkable compositions disclosed in theabove-referenced North et al and Biggs et al patents. These lubricants,in addition to facilitating processing, are considered to be importantto improve the stripping properties of the wire or cable insulation andinclude fatty acid soaps, such as calcium stearate and aluminumstearate, silicone oils, long-chain aliphatic amides, natural andsynthetic waxes and low molecular weight polyethylene. A particularlyuseful lubricant combination disclosed in U.S. Pat. No. 4,349,605 foruse in radiation curable polymeric compositions is a mixture of lauricacid and ethylene-bis-stearamide.

Generally speaking, extrusion coating of wire and cable is not limitedby the equipment used but rather by the processability of the insulationcompositions. If compositions having improved processability wereavailable, the output of most coating lines could be significantlyincreased. It is therefore a continuing objective within the wire andcable industry to improve processability of insulation compositions sothat line speeds can be increased. This, of course, must be accomplishedwithout significantly altering the physical properties of the insulationmaterial.

Heretofore it has not been possible to significantly improveprocessability of highly filled crosslinkable flame retardantcompositions without compromising physical properties or otherwiseadversely affecting the quality of the insulation coating. One cannotsimply increase the amount of a known lubricant additives, such as thelauric acid/EBS lubricant package. While this may facilitate blending,it creates other problems. For example, it can lead to exudation of oneof the lubricants or other additive, contribute to "die drool", andcause surging. "Die drool" is an undesirable build up of extrudate onthe lips of the die. During operation, these build ups periodicallyrelease and are transferred to the surface of the insulated wire forminglumps or rings on the insulated wire. In assembling the insulated wireinto wiring harnesses, the section of wire containing theseimperfections must be cut out and discarded. In extreme instancessurging is obtained which results in the application of an insulationcoating of uneven thickness. Too thick an application of insulationresults in increased manufacturing costs whereas an inadequate thicknessof the insulation layer will result in burn through and shorting. Anexcessive amount of lubricant can also significantly decrease thephysical properties of the crosslinked composition and make it difficultor impossible to obtain the mechanical shear required to adequately mixthe composition in an intensive mixer.

It has now been discovered that by utilizing a low molecular weightprocessing additive, by itself or in combination with other knownprocessing aids, that processability of these crosslinkable formulationscan be significantly improved without the adverse effects heretoforeobtained. Additionally, a surprising increase in resistance to scorchand increased heat stability of the crosslinked product are observed.Whereas some improvement in processability might be predicted by the useof these polymeric processing agents, a significant increase in thescorch time without decreasing total cure and a significant increase inthe heat stability of the composition after crosslinking are totallyunexpected.

Useful polymeric processing agents for the invention are predominantlyaliphatic resins having an average molecular weight less than about 2000and containing ester functional groups. The resins are a mixture ofoligomers. While the molecular weight distribution of the polymericproducts can vary, predominant oligomers will have molecular weightsbelow 2000. A portion of the oligomers comprising the aliphatic resinmixture contain ester functional groups, such as acetoxy groups. Theresin mixtures are solid materials having specific gravities from about0.92 to about 0.98 and softening points from about 90° C. to about 110°C. They exhibit good solubility in aliphatic, aromatic and chlorinatedhydrocarbons.

Low molecular weight polymeric processing additives of the above typeare conveniently obtained by combining an aliphatic hydrocarbon resinderived from petroleum cracking streams with an ester-containing resin.Both the hydrocarbon resin and ester-containing resin are comprised ofoligomers having molecular weights less than 2000. The ratio of thehydrocarbon resin to ester-containing resin can vary widely depending onthe particular resins used. Most commonly, the mixture will contain from50 to 95% of the hydrocarbon resin and 5 to 50% of the ester-containingresin. More preferably, the hydrocarbon resin will comprise 60 to 92% ofthe mixture with the ester-containing resin comprising the balance.

Aliphatic hydrocarbon resins utilized for the polymeric processingadditive are well known and commercially available. They are produced bythe Friedel-Crafts catalyzed polymerization of various mixed olefinstreams obtained from petroleum cracking operations. Resin propertieswill vary depending on composition of the feedstock, the particularcatalyst used and reaction conditions. Hydrocarbon resins used for thepolymeric processing additives are derived from primarily aliphaticolefin monomers. Most advantageously they are produced from feedstocksreferred to within the industry as C-5 streams since this approximatesthe average number of carbon atoms per monomer molecule.

The ester-containing resin present with the hydrocarbon resin to make upthe polymeric processing modifier is typically an olefin-vinyl estercopolymer. Ethylene-vinyl ester copolymers are especially advantageouswith ethylene-vinyl acetate copolymers being particularly preferred.Vinyl acetate contents of these copolymers will range from 12 to 32%and, more commonly, from 15 to 25%.

Minor amounts of other low molecular weight resins, such aspolyethylene, may also be present with the hydrocarbon resin andolefin-vinyl ester copolymer. The oligomer mixtures comprising thepolymeric processing modifiers will typically contain 80-90%C, 8-15%Hand 0.5-7%O. Polymeric processing modifiers meeting the aboverequirements are commercially available from Struktol Company under thedesignations Struktol Polydis® TR060 and Struktol Polydis® SA9001.

To obtain the necessary balance of processability and physicalproperties required for most wire and cable applications, it isgenerally advantageous to include one or more additional processing aidswith the polymeric resin processing modifier. While any known processingagent can be employed for this purpose, superior results have beenobtained when these materials are fatty acids or fatty acid derivativessuch as metal soaps, esters, ester-soaps, amides, and the like. The termfatty acid as employed herein, refers to aliphatic carboxylic acidshaving from 8 to 22 carbon atoms. While these acids are usually derivedfrom natural sources, they can also be synthetically produced. The fattyacids can be branched or straight-chain, saturated or unsaturated andthey may consist of a single acid, or as is more commonly the case, amixture of acids within the specified carbon content range. Illustrativefatty acids include caproic acid, caprylic acid, capric acid, lauricacid, myristic acid, myristoleic acid, palmitic acid, palmitoleic acid,stearic acid, isostearic acid, oleic acid, linoleic acid, eleostearicacid, behenic acid, erucic acid and the like. Useful fatty acid mixturesare obtained from triglycerides present in natural fats and oilsincluding coconut oil, cottonseed oil, linseed oil, palm oil, soy oil,tall oil, safflower oil, corn oil, rapeseed oil, tallow or the like.

While the fatty acids or mixtures may be utilized as such they are morecommonly employed in their derivative forms. Alternatively, a mixture offatty acid and fatty acid derivative can be used. Especially usefulfatty acid derivatives which can be used, alone or in admixture with thesame or different fatty acid, are the calcium or aluminum soaps andamides, including bis-amides formed by the reaction of two moles of afatty acid or fatty acid ester with one mole of an aliphatic diamine,e.g., ethylene diamine. It is necessary to avoid soaps which interferewith the crosslinking reaction (a free radical mechanism), such as zincsoaps, and which react with organic peroxides. Acceptable soaps are thealkaline earth metal fatty acid soaps and calcium stearate has beenfound to be particularly advantageous. Erucamide andethylene-bis-stearamide are particularly useful fatty acid amides. Inone highly useful embodiment of the invention, the fatty componentconsists of a mixture of a fatty acid with a fatty acid amide present ina ratio from 2:1 to 1:10. Combinations of lauric acid andethylene-bis-stearamide are most notable in this regard. If a fattycomponent is employed with the polymeric resin to comprise a processingadditive package, the ratio of fatty acid (or derivative) to aliphaticpolymer resin will range from 3:1 to 1:8 and, more preferably, from 2:1to 1:5.

Also, since it is often advantageous to utilize a mixture of lubricantswith different melting points and chemical structures, natural orsynthetic hydrocarbon waxes or low molecular weight polyethylenes canfunction as part of a lubricant system to obtain the desired balance ofprocessing properties.

COMBINING THE COMPONENTS

The compositions of the invention may be formed in a number of waysprovided that the filler and silane are intimately contacted. The silanemay be added directly to the filler and dispersed in the polymer using ahigh shear internal mixer such as a Banbury, Farrel Continuous Mixer,Bolling Mixtrumat™ or Werner & Pfleiderer mixer and the antioxidant,lubricant and processing agent then added. Alternatively, the silane isfirst added to the polymer followed by addition thereto of the filler,antioxidant, lubricant, processing agent and any other additives. Allcompounding ingredients can be charged to the mixer at the initiation ofmixing as long as the silane and filler have intimate contact during themixing process.

The hydrated inorganic filler in the composition can be varied withinwide limits. The filler can range from 80 to 400 parts per 100 parts ofthe polymer resin (phr). Most commonly, from 80 to 200 phr of filler isemployed. The alkoxysilane will range from about 0.5 to 5 phr and, morepreferably, from 0.75 to 4 phr. Too small an amount may be insufficientto provide adequate surface treatment of the filler while too large aquantity can have an adverse effect on physical properties, primarilypercent elongation, after crosslinking.

The antioxidant or antioxidant package will be selected to meet theservice requirements for the particular polymer being used but willgenerally be present from 0.5 to 8 phr and, more preferably, from 1 to 6phr. Higher levels of antioxidant are required for high temperature wireand cable applications. If two or more antioxidants are employed theymay be added to the formulation separately or combined prior toincorporation.

From 0.25 to 8 phr of the polymeric processing additive is utilized. Forreasons not completely understood, use of the mixed aliphatic resin byitself or in combination with 0.25 to 5 phr fatty acid or fatty acidderivative or mixture thereof significantly improves properties in boththe uncrosslinked and crosslinked composition. The uncrosslinkedcompositions exhibit improved processability; particularly, the timebefore the onset of scorch under the processing conditions issignificantly increased. This provides the processor with greaterflexibility in the selection of operating conditions and, in some cases,makes it possible to increase the line speed of the coating operation.The broadened operating window also makes it possible to accommodateunanticipated changes in processing conditions which frequently occurand which can result in the production of unacceptable product orcatastrophic failure, i.e. blowing the extruder head or freeze-up of theextruder. Upon crosslinking, the compositions develop acceptablephysical properties and, quite unexpectedly, the essential physicalproperties are retained for a longer period upon heat aging. In aparticularly useful embodiment of the invention, 1 to 6 phr of acombination of processing additives comprised of the polymericprocessing agent, i.e., the mixed aliphatic resin, a fatty acid and afatty acid amide are employed.

In addition to the previously mentioned mixers, other processing devicesknown to the art capable of intimately mixing the essential componentsmay be used. The compositions may also contain other additives, such ascarbon black, pigments and the like, provided they do not interfere withcrosslinking or detract from the physical properties of the composition.The total amount of any additional ingredients will generally not exceedabout 15 phr. In one highly useful embodiment of the invention, from 1to 8 phr of a chemical crosslinking agent is included in theformulation.

The ethylene-vinyl ester and ethylene-alkyl acrylate copolymersformulated as hereinabove described can be crosslinked usingconventional procedures known to the art, such as by high-energyirradiation or by the use of chemical crosslinking agents. Fullycrosslinked, these polymers exhibit thermoset behavior and provide asuperior and unexpected balance of:

(1) low temperature brittleness, i.e., the compositions do not readilycrack during low temperature movement (ASTM D-746);

(2) heat resistance after aging, i.e., excellent elongation afterextended service at 90° C., 125° C. or even 135° C.;

(3) arcing and tracking resistance as high as 5 KV;

(4) resistance to ignition by flame and flame retardance;

(5) moisture resistance i.e., low mechanical absorption of waterproviding retention of dielectric properties in wet and humidenvironments;

(6) dielectric properties;

(7) oil resistance; and

(8) resistance to industrial chemicals

It has been demonstrated that for low voltage environments, i.e., lessthan 5000 volts and more commonly less than 600 volts, the compositionsof this invention are particularly useful for service as uniinsulation.Uniinsulation is an art accepted term denoting insulation where onelayer is extruded around a conductor. This single layer serves as theelectrical insulation and the jacketing to provide physical and flameprotection. The present compositions are especially well suited forservice as uniinsulation where a superior balance of properties isrequired. It has been observed that the compositions can contain a highloading of filler and still provide high flexibility and a high degreeof crosslinking. Moreover, the ability to achieve high filler loading,flexibility and crosslinking with improved processability and heat agingis a significant advance in the wire and cable insulation art.

Any means known for crosslinking ethylene copolymers can be utilizedwith the compositions of this invention. While it is possible tothermally crosslink the compositions, it is more common to utilize asource of high energy ionizing radiation or a chemical agent for thispurpose.

High energy radiation sources which can be used to crosslink thesecompositions include cobalt-60, β-rays, γ-rays, x-rays, electron beams,accelerators or the like. Electron beam radiation is a particularlyadvantageous method of radiation crosslinking. The art of radiationcrosslinking is so highly developed that little need be said withrespect to such procedures. As higher total doses of radiation are used,the degree of crosslinking generally increases. For effectivecrosslinking a total radiation dose of about 5 to 25 megarads isgenerally required.

Chemical crosslinking can be accomplished by the use of conventionalagents known to generate free radicals upon decomposition. Organicperoxides are most commonly employed for this purpose. In view of theability to rapidly achieve high levels of cure using chemicalcrosslinking agents and the uniformity of the results obtainabletherewith, this method is widely practiced to cure wire and cableinsulation. Chemical crosslinking is accomplished by incorporating theorganic peroxide or other crosslinking agent into the composition at atemperature below the decomposition temperature of the crosslinkingagent. The chemical agent is later activated to cure the composition,i.e., crosslink the ethylene copolymer into a three-dimensional network.

This crosslinking is carried out in accordance with procedures wellknown to the art and variations in the general conditions necessary toeffect same will be apparent to those skilled in the art. The inventionis not limited to the use of organic peroxides for chemicalcrosslinking--other art recognized materials which decompose to providefree radicals can also be used. Obviously such crosslinking agentsshould not decompose during compounding. Known crosslinking coagents,such as triallylcyanurate and the like, may also be included to increasethe effectiveness of the cure.

Tertiary organic peroxides are especially useful chemical crosslinkingagents. Dicumyl peroxide and alpha, alpha'-bis(t-butylperoxy)diisopropylbenzene are particularly advantageous. As with most otherchemical crosslinking agents, the tertiary organic peroxides areactivated by heating to above their activation temperature whereupondecomposition occurs. Any of the known procedures to accomplishdecomposition, such as the application of high pressure steam or thelike, can be used.

The crosslinking is generally carried out at superatmospheric pressures,on the order of 100 psi to 400 psi, although higher or lower pressuresmay be used. Pressure is employed to avoid developing porous crosslinkedcompositions which are unsuitable for electrical insulation.

In general, as the amount of crosslinking agent is increased the degreeof crosslinking increases. Usually, no more than about 8 phr organicperoxide is necessary and, most preferably, 1.5 to 5 phr peroxide isused. Other crosslinking agents may require some variation in the amountused. The higher the degree of crosslinking, the greater is thetoughness and the greater is the resistance to moisture and chemicalreagents of the polymeric composition. When too low a degree ofcrosslinking is achieved, the physical properties of the product areinadequate and subject to pronounced deterioration upon aging.Insufficient crosslinking results principally in a deficiency inretention of stiffness at elevated temperature since the material willhave too low a softening point. The exact degree of crosslinking istherefore varied to take the above factors and their effect on the finalproduct into account. For wire and cable insulation the level ofcrosslinking is generally greater than 80% although lower values arepossible. Crosslinking is determined by extraction of the crosslinkedpolymer to measure the amount of insoluble gel. Crosslinking levels of85% to 95% are most typical.

EXAMPLES

Various aspects of the invention are described in greater detail in theexamples which follow. These examples are for illustration purposes onlyand are not intended to limit the invention. Numerous variations arepossible without deviating from the spirit and scope of the inventionand will be apparent to those skilled in the art.

To prepare the formulations used in the examples the ingredients wereadded to a Banbury mixer and mixed at a temperature below thedecomposition temperature of the peroxide, usually about 110°-125° C.,until a homogeneous mixture was obtained. Generally, to achieve uniformdispersion of the compounding ingredients in the copolymer requiredabout 3-5 minutes mixing. The mixture was then extruded to obtain theproduct in pellet form. A conventional extruder fitted with an extruderdie and an underwater pelletizer was employed for this operation. Thepelletized product was recovered and utilized for subsequentevaluations.

Physical properties (tensile and elongation) of the products weredetermined in accordance with ASTM D-638. Samples were cured for 6minutes in a compression mold maintained at 250 psi and 200°-205° C.Under these conditions, cures of 80% or greater with tensile strengthsof at least 1800 psi, and more generally greater than 2000 psi, andelongations greater than 200% are typically achieved. The cure level (%gel) was determined in accordance with ASTM D-2765, Method C.

Resistance to thermal aging was determined by heating samples in aforced-air circulating oven for extended periods up to as long as 60days. Since the samples become brittle as they deteriorate in the heataging process, the extent of deterioration was determined by observingthe decrease in elongation with time. Products are considered to bemarginal when upon heat aging the elongation drops below 175% or the %retention of the unaged elongation falls below 75%. For compositionsdesigned for 125° C. continuous service, accelerated heat aging testswere conducted at 158° C. Accelerated heat aging tests were carried outat 165° C. for compositions formulated for 135° C. continuous serviceand at 180° C. for 150° C. continuous service.

For meaningful comparison of physical properties of different products,the degree of cure of the products being compared should be 80% orgreater and, preferably, within 5% of each other. Electrical properties(dielectric constant and dissipation factor) of cured compositions weredetermined in accordance with ASTM D-150

Extrusion evaluations were performed using a 1 inch diameter Brabenderextruder having three electrically heated zones and an air-cooledbarrel. The extruder had a 20:1 length to screw diameter ratio. Apolyethylene-type screw with 20 flites and a 4:1 compression ratio wasemployed and a pressure gauge was located at the end of the screw at thelocation where a breaker plate is normally employed. The extruder wasequipped to measure the torque required to process the material.

A Brabender wire insulating die assembled for the insulation of 18 AWGwire was employed with a wire inserted through and fixed in the die.While the wire was not pulled through the die for these laboratoryextrusions, a strand was produced with the same restrictions at the dieorifice as encountered during wire insulation using production units.

The extruder barrel zones 1, 2, and 3 were set at 210° F., 220° F., and230° F., respectively, and the die temperature was set at 230° F. Screwspeed was maintained at 100 rpm. These conditions effectively measurethe relative processability of different insulation compositions and thetendency of the materials to increase temperature at the compressionarea (zone 2) of the screw. Temperatures, head pressure and torque wererecorded versus time to measure the relative ability of materials to beprocessed at high extrusion speed without developing scorch, i.e.,prematurely crosslinking. When the temperature in zone 2 increased to295°-300° F. the crosslinked material was quickly purged withuncompounded copolymer resin to avoid freeze-up of the extruder withcrosslinked material. This temperature is the point where catastrophicuncontrolled crosslinking begins to occur. If unchecked, this willresult in the formation of an intractable product incapable of beinguniformly flowed onto a wire or cable and ultimately can freeze-up theextruder. With some control materials, the heat build up was so rapidthat considerable scorching could not be avoided. Between each extrusionrun, the extruder was purged with uncompounded resin until the initialoperating conditions were again reached.

Example I: To demonstrate the significantly improved resistance to heataging obtained with compositions prepared in accordance with the presentinvention utilizing a polymeric processing agent, three formulationswere prepared and evaluated from the following masterbatch:

    ______________________________________                           Parts    ______________________________________    Ethylene-Vinyl Acetate Copolymer                             100.0    Hydrated Alumina         125.0    Vinyltrimethoxysilane    1.5    Tetrakis(methylene(3,5-di-t-butyl-4-                             2.0    hydroxyhydrocinnamate)) methane    Distearyl-3,3'-thiodipropionate                             1.0    Alpha, alpha'-bis(t-butylperoxy)diisopropyl                             1.7    benzene    ______________________________________

The EVA copolymer used contained 18% VA and had an MI of 2.3 to 2.5. Theabove composition was formulated with a polymeric processing agent(Struktol Polydis® TR060) at two different levels. The polymericprocessing agent is a mixture comprised predominantly of a major portionof petroleum resin oligomers and a minor amount of acetoxy-containingoligomers, the predominant oligomers of both the hydrocarbon resin andthe ester-containing resin having molecular weights less than 2000. Themixed light amber resin had a specific gravity of about 0.95, softeningpoint of about 102° C., flash point greater than 230° C. and TGA (5%loss) of 325° C. The mixed resin processing agent is comprisedpredominantly of carbon and hydrogen (approx. 87%C and 12%H) withapproximately 1% oxygen and trace amounts of sulfur and nitrogen. Thefirst composition, identified as Product I(A), contained 1 phr of thealiphatic resin mixture and a second composition, identified as ProductI(B), contained 1.5 phr of the mixed aliphatic resin processing agent. Athird composition, identified as Comparison I, contained no polymericprocessing modifier but rather was prepared using a conventionallubricant additive package of the type disclosed in U.S. Pat. No.4,349,605, namely, 0.25 phr lauric acid and 0.75 phrethylene-bis-stearamide. Samples were prepared from each composition andcured to 93±2%. Tensile and elongation properties of the samples weredetermined initially and then after aging for 18 days at 163° C. Resultswere as follows:

    ______________________________________                   Prod.  Prod.    Comp.                   I (A)  I (B)    I    ______________________________________    Initial Physical Properties:    Tensile (psi)    2900     2800     2980    Elongation(%)    200      220      200    Physical Properties    After Heat Aging:    Tensile (psi)    2760     2780     2030    % Retention of Unaged Tensile                     95.2     99.3     68.1    Elongation (%)   180      190      100    % Retention of Unaged                     90.0     86.4     50.0    Elongation    ______________________________________

The above results clearly demonstrate the improved heat stability of theresulting cured compositions prepared using the aliphatic resinprocessing agent. The compositions containing the aliphatic resin exceedthe 175% elongation minimum after the 18 day aging interval whereas theproduct prepared using the conventional lubricant additive package isfar below the 175% elongation standard. Expressed differently, there isa 50% reduction in the elongation of the control composition after 18days aging at 163° C. whereas the elongation of Products I(A) and I(B)decreased only 10% and 13.6%, respectively. Comparable results areobtained when a mixed aliphatic resin processing aid having asubstantially higher ester content based on elemental analysis, StruktolPolydis® SA9001, is substituted into the above formulations.

Example II: To demonstrate the ability to utilize the polymericprocessing agent in combination with other conventional processing aids,the following formulation was prepared:

    ______________________________________                           Parts    ______________________________________    EVA Copolymer of Example I                             100.0    Hydrated Alumina         125.0    Vinyltrimethoxysilane    1.5    Tetrakis(methylene(3,5-di-t-butyl-4-                             2.0    hydroxyhydrocinnamate)) methane    Distearyl-3,3'-thiodipropionate                             1.0    Alpha, alpha'-bis(t-butylperoxy)diisopropyl                             1.7    benzene    Lauric Acid              0.25    Ethylene-bis-stearamide  0.75    Polymeric Resin Processing Agent                             1.0    ______________________________________

The above ingredients were blended and samples prepared and cured in theconventional manner. Tensile strength of the cured composition was 2200psi with an elongation of 230%. After aging for 18 days at 163° C. theelongation was still 190% (82.6% retention of the original elongation).The tensile strength of the product after aging was actually higher(2690 psi) than the original value. Such increases in tensile are notuncommon and are believed to be the result of additional curing duringthe heat aging. The above example not only shows the ability to utilizea mixed aliphatic resin processing aid in conjunction with other knownprocessing agents but also demonstrates the ability to raise the heatstability of compositions formulated with conventional lubricants toacceptable levels by the addition of a polymeric processing additivethereto.

Example III: A formulation identical to that of Example II was preparedusing an EVA copolymer containing 18% VA but having an MI of 1.3-1.5.The composition after curing (92.8% gel) had a tensile of 2810 psi andelongation of 250%. Physical properties of the composition after 7, 14,and 18 days aging at 163° C. were as follows:

    ______________________________________    7 Days:    Tensile (psi)         3100    % Retention of Unaged Tensile                          110.3    Elongation (%)        230    % Retention of Unaged Elongation                          92.0    14 Days:    Tensile (psi)         2840    % Retention of Unaged Tensile                          101.1    Elongation (%)        190    % Retention of Unaged Elongation                          76.0    18 Days:    Tensile (psi)         2620    Retention of Unaged Tensile                          93.2    Elongation (%)        170    % Retention of Unaged Elongation                          68.0    ______________________________________

Where the % elongation after 18 days aging is considered to be onlymarginally acceptable, it is a significant improvement over the 70%elongation obtained with a control containing no aliphatic resinprocessing agent. The 70% elongation obtained for the control representsonly 39% retention of the original (unaged) elongation value.

Example IV: A series of compositions were prepared with varying levelsof aliphatic resin processing agent in accordance with the followingrecipes:

    ______________________________________    Product No.  IV(A)   IV(B)   IV(C) IV(D) IV(E)    ______________________________________    EVA Copolymer                 100.0   100.0   100.0 100.0 100.0    (18% VA; MI 1.3-1.5)    Hydrated Alumina                 125.0   125.0   125.0 125.0 125.0    Vinylmethoxysilane                 1.5     1.5     1.5   1.5   1.5    Tetrakis(methylene                 1.0     1.0     1.0   1.0   1.0    (3,5-di-t-butyl-4-    hydroxyhydro-    cinnamate))    methane    Bis Alkyl Sulfide                 2.0     2.0     2.0   2.0   2.0    (ANOXSYN ™ 442)    Alpha, alpha'-bis                 1.7     1.7     1.7   1.7   1.7    (t-butylperoxy)    diisopropyl benzene    Lauric Acid  0.25    0.25    0.25  0.25  0.25    Ethylene-bis-                 0.75    0.75    0.75  0.75  0.75    stearamide    Mixed Aliphatic Resin                 0.5     1.0     2.0   3.0   5.0    Processing Agent    ______________________________________

Processability of each of the above formulations was evaluated inaccordance with the previously described procedure using the Brabenderextruder. Head pressure and torque were measured for each sample and arereported in Table I. Time (in minutes) required for the temperature inZone 2 (the compression zone) to reach 290° F. was also recorded. Thisis an indication of the length of time the composition can be processedunder operating conditions before crosslinking begins to occur. Theproblems associated with premature crosslinking in the extruder havepreviously been pointed out. Additionally, visual observation of theextrudate was made and the time at which the first indication

                  TABLE I    ______________________________________    Product No.  IV(A)   IV(B)   IV(C) IV(D) IV(E)    ______________________________________    Extrusion Data:    Head Pressure (psi)                 6200    6150    6000  5900  5650    Torque (meter-grams)                 4550    4550    4500  4450  4400    Time for Temperature                 8       8       9     10+   10+    in Zone 2 to reach    290° F. (minutes)    Time to Scorch                 9+      9+      10+   10+   10+    (minutes)    Cure Level (%)                 92.9    92.4    91.8  90.7  88.6    Physical Properties:    (Unaged)    Tensile (psi)                 3060    3040    2850  2930  2700    Elongation (%)                 240     220     200   260   210    Physical Properties:    (heat-aged):    Tensile (psi)                 3020    3140    3060  2990  2920    % Retention of                 98.7    103.3   107.4 102.0 108.1    Unaged Tensile    Elongation (%)                 190     220     220   220   220    % Retention of Unag-                 79.2    100.0   110.0 84.6  104.8    ed Elongation    Electrical Properties:    Dielectric Constant                 3.75    3.76    3.77  3.78  3.77    (1,000 Hz)    Dissipation Factor                 .0080   .0082   .0079 .0077 .0074    (1,000 Hz)    ______________________________________

of roughness or unevenness appeared was recorded and is reported in thetable as the time to scorch. Times provided in the table which arefollowed by a plus sign indicate that the extrusion was terminate before290° F. was reached or before visual scorching of the extrudate wasobserved.

Each formulation was also cured in accordance with the conventionalprocedure and evaluated for resistance to heat aging. Electricalproperties of the cured products were also determined. Results are setforth in the table. Heat aging data reported are for 18 days at 163° C.The cure level (% gel) was determined for each sample and indicated.

For comparison, a control composition containing all of the ingredientsexcept the aliphatic resin processing agent was extruded under identicalconditions. The head pressure obtained for the control was 6400 psi andthe torque was 4750 meters-grams. The temperature in Zone 2 of theextruder rose to 290° F. in less than three minutes with the control andvisual scorching of the extrudate was observed after only three minutesoperation. It is apparent from the foregoing comparative data that asignificant improvement in resistance to scorch is obtained with thecompositions of the invention containing an aliphatic resin.Furthermore, when an aliphatic resin is included with conventionalprocessing additives, there is a slight reduction of head pressure andtorque. Similar improvement is obtained using a commercially availablemixed aliphatic resin processing modifier having a substantially higherester (acetoxy) content, i.e., approximately 5% oxygen by analysis.

Example V: A mixed resin comprised of an ethylene-vinyl acetatecopolymer and ethylene-n-butyl acrylate copolymer was formulated asfollows:

    ______________________________________                      Parts    ______________________________________    EVA Copolymer       80.0    (18% VA; MI 1.3-1.5)    EBA Copolymer       20.0    (19% BA; MI 0.3)    Hydrated Alumina    125.0    Vinyltrimethoxysilane                        1.5    Tetrakis(methylene  1.0    (3,5-di-t-butyl-4-    hydroxyhydrocinnamate))    methane    Bis Alkyl Sulfide   2.0    (ANOXSYN ™ 442)    Alpha, alpha'-bis   1.7    (t-butylperoxy)    diisopropyl benzene    Lauric Acid         0.25    Ethylene-bis-stearamide                        0.75    ______________________________________

Three compositions containing varying levels of polymeric resinprocessing agents were prepared using the above formulation andevaluated in accordance with the procedure described in Example IV.Results are set forth in Table II. Similar results are obtained whenblends of EVA and low-density polyethylene are comparably formulated.

                  TABLE II    ______________________________________    Product No.         V(A)    V(B)     V(C)    ______________________________________    Aliphatic Resin (phr)                        1.0     2.0      3.0    Extrusion Data:    Head Pressure (psi) 6800    6700     6300    Torque (meter-grams)                        4900    4900     4650    Time for Temperature in                        8       9        9    Zone 3 to reach 290° F. (min)    Time to Scorch (min)                        8+      10+      10+    Cure Level (%)      92.3    90.5     89.4    Physical Properties: (unaged)    Tensile (psi)       2940    2870     2830    Elongation (%)      220     250      250    Physical Properties:    (heat aged 30 days at 163° C.)    Tensile (psi)       2880    2930     2840    % Retention of Unaged Tensile                        98.0    102.1    100.4    Elongation (%)      210     220      210    % Retention of Unaged Elongation                        95.5    88.0     84.0    Electrical Properties:    Dielectric Constant (1,000 Hz)                        3.80    3.75     3.75    Dissipation Factor (1,000 Hz)                        .0066   .0074    .0066    ______________________________________

Example VI: A wire and cable insulation composition similar to that ofExample V but designed for 150° C. continuous service was formulated inaccordance with the following recipe:

    ______________________________________                       Parts    ______________________________________    EVA Copolymer        80.0    (18% VA; MI 1.3-1.5)    EBA Copolymer        20.0    (19% BA; MI 0.3)    Hydrated Alumina     125.0    Vinyl alkoxysilane   1.5    High Temperature Stabilizer                         5.6    Package (Antioxidant)    Organic Peroxide     1.7    Lauric Acid          0.25    Ethylene-bis-stearamide                         0.75    Polymeric Processing Modifier                         1.0    ______________________________________

The above composition was cured and had a tensile strength of 2340 psiand elongation of 280%. Samples of the product were aged at 180° C. andtensile and elongation properties of the vulcanizate determined after 7and 14 days. Results were as follows:

    ______________________________________    7 Days:    Tensile (psi)         2280    % Retention of Unaged Tensile                          97    Elongation (%)        210    % Retention of Unaged Elongation                          75    14 Days:    Tensile (psi)         2570    % Retention of Unaged Tensile                          109.8    Elongation (%)        200    % Retention of Unaged Elongation                          71.4    ______________________________________

We claim:
 1. A electrical conductor coated with an insulating layer of acrosslinkable polymer composition comprising(a) a polymer selected fromthe group consisting of copolymers of ethylene and vinyl esters of C₂₋₆aliphatic carboxylic acids, copolymers of ethylene and C₁₋₆ alkylacrylates, copolymers of ethylene and C₁₋₆ alkyl methacrylates, ormixtures thereof; (b) 80 to 400 phr inorganic filler selected from thegroup consisting of hydrated aluminum oxide, hydrated magnesia, hydratedcalcium silicate, and hydrated magnesium carbonate; (c) 0.5 to 5 phr ofa lower alkyl-, alkenyl-, alkynyl- or aryl-alkoxysilane having from 1 to3 C₁₋₆ alkoxy substituents; (d) 0.5 to 8 phr antioxidant; and (e) 0.25to 8 phr low molecular weight polymeric processing additive comprised ofaliphatic resins having an average molecular weight less than 2000 andcontaining ester functional groups.
 2. The coated electrical conductorof claim 1 wherein (a) is ethylene-vinyl acetate copolymer,ethylene-butyl acrylate copolymer, or mixtures thereof, (d) is a thiocompound, a hindered phenol, polymerized, 1,2-dihydro-2,2,4-trimethylquinoline, tris(3,5-di-t-butyl-4-hydroxy benzyl)isocyanurate or mixturesthereof and (e) is a mixture of hydrocarbon resin oligomers andester-containing resin oligomers and wherein the predominant oligomershave molecular weights less than
 2000. 3. The coated electricalconductor of claim 2 wherein the conductor is copper wire.
 4. The coatedelectrical conductor of claim 3 wherein the crosslinkable polymericcomposition additionally contains from 1 to 8 phr of a chemicalcrosslinking agent.
 5. The coated electrical conductor of claim 4wherein the chemical crosslinking agent is an organic peroxide, (c) is avinyl alkoxysilane, (e) has a specific gravity from 0.92 to 0.98 andsoftening point from 90° C. to 110° C. and additionally containing 0.25to 5 phr of a second processing additive selected from the groupconsisting of a fatty acid, a calcium soap of a fatty acid, an aluminumsoap of a fatty acid, a fatty acid amide, a mixture of a fatty acid anda fatty acid amide, a natural or synthetic wax and low molecular weightpolyethylene.
 6. The coated electrical conductor of claim 5 containing80 to 200 phr (b), 0.75 to 4 phr (c), 1 to 6 phr (d), 0.25 to 5 phr (e)and 1.5 to 5 phr organic peroxide.
 7. The coated electrical conductor ofclaim 6 wherein (a) is an ethylene-vinyl acetate copolymer having from9% to 30% vinyl acetate polymerized and a melt index from 0.5 to
 5. 8.The coated electrical conductor of claim 6 wherein (b) is hydratedalumina.
 9. The coated electrical conductor of claim 6 wherein (c) isvinyltrimethoxysilane.
 10. The coated electrical conductor of claim 6wherein (d) is a mixture of distearyl-3,3'-thiodipropionate andtetrakis(methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)) methane.11. The coated electrical conductor of claim 6 wherein (d) is a mixtureof a bis alkyl sulfide and tetrakis(methylene(3,5-di-ti-butyl-4-hydroxyhydrocinnamate)) methane.
 12. The coatedelectrical conductor of claim 6 wherein the organic peroxide is dicumylperoxide.
 13. The coated electrical conductor of claim 6 wherein theorganic peroxide is alpha, alpha'-bis(t-butylperoxy)diisopropyl-benzene.
 14. The coated electrical conductor of claim 6 wherein thesecond processing agent is a mixture of ethylene-bis-stearamide andlauric acid.
 15. The coated electrical conductor of claim 6 wherein (e)is a mixture of aliphatic hydrocarbon oligomers produced by thepolymerization of a mixed olefin feed obtained from petroleum crackingwith a minor amount of an olefin-vinyl ester copolymer.
 16. The coatedelectrical conductor of claim 7 wherein (a) contains 12 to 32 percentvinyl acetate.